44 research outputs found
Artificial ferroelectricity due to anomalous Hall effect in magnetic tunnel junctions
We theoretically investigated Anomalous Hall Effect (AHE) and Spin Hall
Effect (SHE) transversally to the insulating spacer O, in magnetic tunnel
junctions of the form F/O/F where F are ferromagnetic layers and O represents a
tunnel barrier. We considered the case of purely ballistic (quantum mechanical)
transport, taking into account the assymetric scattering due to spin-orbit
interaction in the tunnel barrier. AHE and SHE in the considered case have a
surface nature due to proximity effect. Their amplitude is in first order of
the scattering potential. This contrasts with ferromagnetic metals wherein
these effect are in second (side-jump scattering) and third (skew scattering)
order on these potentials. The value of AHE voltage in insulating spacer may be
much larger than in metallic ferromagnetic electrodes. For the antiparallel
orientation of the magnetizations in the two F-electrodes, a spontaneous Hall
voltage exists even at zero applied voltage. Therefore an insulating spacer
sandwiched between two ferromagnetic layers can be considered as exhibiting a
spontaneous ferroelectricity
Does Giant Magnetoresistance Survive in Presence of Superconducting Contact?
The giant magnetoresistance (GMR) of ferromagnetic bilayers with a
superconducting contact (F1/F2/S) is calculated in ballistic and diffusive
regimes. As in spin-valve, it is assumed that the magnetization in the two
ferromagnetic layers F1 and F2 can be changed from parallel to antiparallel. It
is shown that the GMR defined as the change of conductance between the two
magnetic configurations is an oscillatory function of the thickness of F2 layer
and tends to an asymptotic positive value at large thickness. This is due to
the formation of quantum well states in F2 induced by Andreev reflection at the
F2/S interface and reflection at F1/F2 interface in antiparallel configuration.
In the diffusive regime, if only spin-dependent scattering rates in the
magnetic layers are considered (no difference in Fermi wave-vectors between
spin up and down electrons) then the GMR is supressed due to the mixing of spin
up and down electron-hole channels by Andreev reflection.Comment: 7 pages, 4 figures, submitted to Phys.Rev.Let
Spin-dependent diffraction at ferromagnetic/spin spiral interface
Spin-dependent transport is investigated in ballistic regime through the
interface between a ferromagnet and a spin spiral. We show that spin-dependent
interferences lead to a new type of diffraction called "spin-diffraction". It
is shown that this spin-diffraction leads to local spin and electrical currents
along the interface. This study also shows that in highly non homogeneous
magnetic configuration (non adiabatic limit), the contribution of the
diffracted electrons is crucial to describe spin transport in such structures
Analytical description of ballistic spin currents and torques in magnetic tunnel junctions
In this work we demonstrate explicit analytical expressions for both charge
and spin currents which constitute the 2x2 spinor in magnetic tunnel junctions
with noncollinear magnetizations under applied voltage. The calculations have
been performed within the free electron model in the framework of the Keldysh
formalism and WKB approximation. We demonstrate that spin/charge currents and
spin transfer torques are all explicitly expressed through only three
irreducible quantities, without further approximations. The conditions and
mechanisms of deviation from the conventional sine angular dependence of both
spin currents and torques are shown and discussed. It is shown in the thick
barrier approximation that all tunneling transport quantities can be expressed
in an extremely simplified form via Slonczewski spin polarizations and our
effective spin averaged interfacial transmission probabilities and effective
out-of-plane polarizations at both interfaces. It is proven that the latter
plays a key role in the emergence of perpendicular spin torque as well as in
the angular dependence character of all spin and charge transport considered.
It is demonstrated directly also that for any applied voltage, the parallel
component of spin current at the FM/I interface is expressed via collinear
longitudinal spin current components. Finally, spin transfer torque behavior is
analyzed in a view of transverse characteristic length scales for spin
transport.Comment: 10 pages, 6 figure
Quasi-Two-Dimensional Extraordinary Hall Effect
Quasi-two-dimensional transport is investigated in a system consisting of one
ferromagnetic layer placed between two insulating layers. Using the mechanism
of skew-scattering to describe the Extraordinary Hall Effect (EHE) and
calculating the conductivity tensor, we compare the quasi- two-dimensional Hall
resistance with the resistance of a massive sample. In this study a new
mechanism of EHE (geometric mechanism of EHE) due to non-ideal interfaces and
volume defects is also proposed.Comment: 14 pages, 5 figures; typos corrected in thickness units (figures 1-5
Resonance magneto-resistance in double barrier structure with spin-valve
The conductance and tunnel magneto-resistance (TMR) of the double barrier
magnetic tunnel junction with spin-valve sandwich (F/P/F) inserted between two
insulating barrier, are theoretically investigated. It is shown, that resonant
tunnelling, due to the quantum well states of the electron confined between two
barriers, sharply depends on the mutual orientation of the magnetizations of
ferromagnetic layers F. The calculated optimistic value of TMR exceeds 2000% .Comment: 3 pages, 4 figure
Influence of s-d scattering on the electron density of states in ferromagnet/superconductor bilayer
We study the dependence of the electronic density of states (DOS) on the
distance from the boundary for a ferromagnet/superconductor bilayer. We
calculate the electron density of states in such structure taking into account
the two-band model of the ferromagnet (FM) with conducting s and localized d
electrons and a simple s-wave superconductor (SC). It is demonstrated that due
to the electron s-d scattering in the ferromagnetic layer in the third order of
s-d scattering parameter the oscillation of the density of states has larger
period and more drastic decrease in comparison with the oscillation period for
the electron density of states in the zero order.Comment: 5 pages, 3 figure